Process for tanned leather and article made with it

Abstract

The present invention relates to a process for tanned leather, particularly for leather intended for the manufacture of soles. The re-tanning process comprises at least one wet treatment, in which a vinyl polymer is used, and a further wet treatment step, in which a fatliquor is used. Said wet treatment steps are followed by a step in which said leather is subjected to vacuum treatment.

Description

[0001] PROCESS FOR TANNED LEATHER AND ARTICLE MADE WITH IT

[0002] DESCRIPTION

[0003] STATE OF THE ART

[0004] The leather used today for the manufacturing of belts, soles and leather goods is a substantially rigid leather, with characteristics functional to a use in which a certain hardness, consistency and resistance to wear are required.

[0005] These characteristics, however, constitute a major drawback when such leather is used in the manufacturing of certain goods, such as footwear, as they negatively affect the perception and the overall experience of the end consumers. In fact, the reduced flexibility and excessive hardness, as well as the slipperiness of footwear produced with such leather, compromise the comfort of the user during prolonged use. As a consequence, the use of this type of leather is confined to the manufacturing of so- called ceremonial footwear, while the task of fulfilling the needs of a big portion of the footwear sector is left to injected polymers and rubbers which make the footwear produced therewith more comfortable during prolonged use.

[0006] Therefore, especially in this sector, the Applicant has perceived that it would be of great interest the realisation of a softer leather, which makes the footwear produced therewith much more pleasant to wear, comfortable to use, while also improving the safety thereof, by greatly increasing their adhesion to walking surfaces. A softer leather would also give the soles, for example, better cushioning when walking, by providing a sort of shock-adsorber effect.

[0007] Ultimately, the Applicant perceived that the availability of a "soft" and flexible leather would also make it possible to manufacture leather sports shoes, thus enabling the realization of footwear that combines the well-known and appreciated natural properties of the leather with those of extreme comfort of the rubber.

[0008] In this regard, the Applicant has observed that to date there is no type of leather on the market, nor is it known in the literature, which possesses the above-described desired characteristics.

[0009] Therefore, the problem of realising a soft leather that, in addition to displaying the required traditional characteristics of consistency and resistance, proves to be, at the same time, soft, flexible and aesthetically free from defects, such as, in particular, stains resulting from poor or uneven penetration of the greasing chemicals used in the process itself, still remains unsolved today.

[0010] SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of the present invention to provide a process for treating leather that allows to obtain soft leather.

[0012] The leather obtained by the process according to the present invention display many advantageous characteristics such as homogeneity and durability, as well as softness, flexibility, and aesthetic value, thereby overcoming technical and functional limitations of tanned leather currently available in the market and / or disclosed in the prior art.

[0013] In one aspect, there is provided a process comprising:

[0014] (i) a wet treatment of tanned leather comprising the following steps:

[0015] (a) bringing the tanned leather into contact with at least one vinyl polymer;

[0016] (b) bringing the tanned leather into contact with at least one fatliquor; and,

[0017] (ii) subjecting the tanned leather obtained from step (i) to a vacuum treatment.

[0018] The Applicant has indeed surprisingly found that by wet treating tanned leather, wherein the wet treatment comprises , in any order, the step of using a vinyl polymer and the step of using a fatliquor, and then subjecting the leather that has undergone the above-mentioned wet treatment to a vacuum treatment, it is possible to obtain high quality, durable leather suitable for many applications. The leather obtained by the process according to the present invention possesses many of the required characteristics to perform well in a variety of manufacturing sectors, such as, for example, the footwear sector.

[0019] Some of the characteristics of the leather obtained by the process according to the present invention are, for example, softness, flexibility, robustness, durability and so on. Advantageously, the leather obtained by the process according to the present invention is also free of stains and displays the aesthetic characteristics that make it suitable for the fashion industry, including for example the footwear sector. In its further aspects, the present invention also relates to leather obtainable by the process according to the present invention, as well as to a shoe sole made with said leather.

[0020] The advantages of the leather and the shoe sole produced with such leather according to these further aspects of the invention have already been highlighted with reference to the first aspect of the invention and are not reiterated here.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention relates to a re-tanning process comprising:

[0023] (i) a wet treatment of tanned leather comprising the following steps:

[0024] (a) bringing the tanned leather into contact with at least one vinyl polymer;

[0025] (b) bringing the tanned leather into contact with at least one fatliquor; and,

[0026] (ii) subjecting the tanned leather obtained from step (i) to a vacuum treatment.

[0027] The Applicant has indeed surprisingly found that such process, as further detailed in the Summary of the Invention, allows to obtain leather that is robust and durable, while also possessing the desired characteristics of softness, flexibility, and aesthetical appearance capable, thereby overcoming technical and functional limitations encountered in the prior art.

[0028] Throughout the present description and in the subsequent claims, all numerical values indicating quantities, parameters, percentages, and so forth are to be understood as preceded in every instance by the term "approximately" unless otherwise indicated. Additionally, all ranges of numerical values include all possible combinations of maximum and minimum numerical values and all possible intermediate ranges, in addition to those specifically indicated below.

[0029] For the purposes of the present invention, tanned leather is to be understood as leather that has already undergone a tanning process of any nature (such as chrome tanning, vegetable tanning, and metal-free tanning), optionally, also already subjected to a re-tanning process.

[0030] A wet treatment refers to a treatment performed in a closed container, typically in a drum, where water is present. The present invention may present, in one or more of its aspects, one or more of the preferred features listed below, which may be combined according to the requirements of specific applications.

[0031] Preferably, in the process according to the present invention, the tanned leather has a thickness equal to or greater than 5 mm.

[0032] Preferably, step (a) of the process according to the invention is conducted at a temperature ranging from 20 to 40 °C, more preferably from 25 to 35 °C, even more preferably approximately 30°C.

[0033] Preferably, the vinyl polymer of step (a) is an acrylic polymer.

[0034] In a preferred embodiment of the invention, said acrylic polymer is used in the form of an aqueous dispersion.

[0035] Preferably, the vinyl polymer in step (a) is used in an amount of at least 2% by weight with respect to the dry weight of the tanned leather.

[0036] The inventors have found that the quantity of polymer to be used to achieve the optimal and desired softening effect also depends on the thickness of the tanned leather to be treated.

[0037] Preferably, for tanned leather thicknesses greater than 5 mm, the quantity of said polymer to be used is at least 5% by weight relative to the dry weight of the tanned leather.

[0038] Preferably, in step (b) of the process according to the present invention, the fatliquor is chosen from the group consisting of sulfonated oil, sulfited oil, and sulfated oil.

[0039] Advantageously, said fatliquor is of vegetable, animal, or mineral origin; preferably, it is an animal-origin sulfited oil, even more preferably a fish-origin sulfited oil.

[0040] Advantageously, said fatliquor is a sulfited oil, preferably of animal origin and even more preferably of fish origin. Such oil is able to more deeply penetrate into the leather fibers and shows a wide resistance to pH fluctuations which makes it suitable for use in many operational conditions.

[0041] Advantageously, when step (b) involves contacting the tanned leather with fish-origin sulfited oil, the leather obtained by the process according to the invention presents an homogeneous surface without any stain (defects instead typically encountered when fatliquors are used in tanning processes).

[0042] Preferably, step (b) of the process according to the invention is performed at a temperature ranging from 30 to 50 °C, more preferably at a temperature of approximately 40 °C.

[0043] Preferably, said fatliquor is used as a formulation comprising at least one surfactant.

[0044] The presence of at least one surfactant promotes emulsification in the processing bath during the aqueous phase.

[0045] In an embodiment, the fatliquor is used in an amount equal to at least 2% by weight with respect to the dry weight of the tanned leather.

[0046] The process according to the invention may optionally involve one or more steps between step (a), i.e. bringing the tanned leather into contact with at least one vinyl polymer and step (b), i.e. bringing the tanned leather into contact with at least one fatliquor. Such steps may include the addition of other products and / or chemicals, that provide additional properties and desired characteristics to the leather.

[0047] Furthermore, in one embodiment the process may involve performing step (a) followed by step (b). In another embodiments, the process may involve performing first step (b) and then step (a).

[0048] Therefore, in a first embodiment the process according to the present invention involves performing, in order, steps (a), (b), and (i).

[0049] In a second and alternative embodiment, the process according to the present invention involves performing, in order, steps (b), (a), and (i).

[0050] Downstream of both steps (a) and (b), the process according to the present invention involves step (i), i.e. subjecting the tanned leather obtained from steps (a) e (b) to a vacuum treatment.

[0051] Preferably, said step (i) is performed at a temperature ranging from 35 to 55 °C, more preferably at a temperature ranging from 40 to 50 °C, even more preferably at a temperature of approximately 45 °C. Preferably, said vacuum treatment has a duration ranging from 2 to 6 minutes, more preferably from 3 to 5 minutes.

[0052] Step (i), i.e. the vacuum treatment, has proven to be particularly important in that it removes residual water from the leather and, at the same time, promotes polymer crosslinking, which promotes the penetration of the polymer into the leather, thereby promoting optimal filling thereof.

[0053] In its further aspects, the present invention also relates to leather obtainable by the process according to the present invention, as well as to a shoe sole for footwear made with said leather.

[0054] The advantages of the leather and shoe sole according to these further aspects of the invention have already been highlighted with reference to the first aspect of the invention and are not repeated here.

[0055] The invention is now illustrated by some Examples which are intended to be illustrative and not limiting the scope of the invention.

[0056] EXPERIMENTAL PART

[0057] Example 1 - leather preparation according to the invention

[0058] A leather obtained from a buffed butt (i.e. a tanned and re-tanned leather) was placed in a vat with an amount of water equal to 100% of its dry weight at a temperature of 30°C. Subsequently, the leather underwent the following series of treatments according to the invention:

[0059] (a) addition of water in an amount of 50% with respect to the dry weight of the leather and of an acrylic polymer (commercial product called SOFTABLE R-GUM) in an amount of 12% with respect to the dry weight of the leather. The water and the acrylic polymer were then left to stir for about 4 hours at a temperature of approximately 30°C; and

[0060] (b) addition of water in an amount of 20% with respect to the dry weight of the leather and of a fish sulfited oil (commercial product called SOFTABLE O-S) in an amount of 5% with respect to the dry weight of the leather. The water and the fish sulfited oil were then left to stir for about 1 hour at a temperature of approximately 40°C. Water in an amount of 30% by weight with respect to the dry weight of the leather was then added, as well as formic acid in an amount of 1 % by weight with respect to the dry weight of the leather, and oxalic acid in an amount of 0.5% by weight with respect to the dry weight of the leather. The water, the formic acid and the oxalic acid were then left to stir for about 1 hour at a temperature of approximately 40°C.

[0061] The water was then drained from the drum, and the leather was first drained off and then subjected to samming to remove any remaining water; the leather obtained in this way was then subjected to shaving operations and finally to a vacuum treatment at a temperature of approximately 45°C for about 3 minutes.

[0062] After further drying, the leather underwent perching / stretching and buffing, thus resulting in the soft leather according to the invention.

[0063] Example 2 - Comparative Tests between the Leather of the Invention and Traditional Leather Obtained through Conventional Process.

[0064] Two samples of leather obtained using the process according to the invention and a standard leather were tested to determine their tensile strength (I.U.P. / 6) and elongation at break.

[0065] In particular, the following samples were tested:

[0066] • A sample of chromium-tanned leather with a thickness of 5 mm subjected to the process according to example 1 (CR);

[0067] • A sample of metal-free tanned leather with a thickness of 5.5 mm subjected to the process according to example 1 (MF);

[0068] • A sample of standard vegetable-tanned leather with a thickness of 5 mm (ST).

[0069] The following results were obtained: As evident from the results reported in the table above, the samples made with the leather according to the invention were performing significantly better in relation to both observation parameters when compared to the sample made with standard leather.

[0070] Particularly significant was the increase in elongation at break (even over 60% in the case of sample MF compared to sample ST), indicating the greater elasticity of the leather made according to the invention.

[0071] Example 3 - Test of Flexing Endurance on the Samples from Example 2.

[0072] The three samples CR, MF, and ST from Example 2 were subjected to the flexing endurance test to repeated flexing of elastomeric and plastic materials for shoe soles (Bennewart and Ross) UN 8921 :2006.

[0073] The method consists of subjecting the sample to 30,000 repeated flexing cycles to verify the sample's ability to withstand stress.

[0074] While in the case of sample ST (the comparison sample), after reaching 30,000 stress cycles, the sample exhibited obvious defects with large areas of folds near tearing, samples CR and MF (both according to the invention) widely withstood these stresses, and at the end of the tests, these samples did not exhibit any defects on their surface, showing the ability to undergo further stress cycles.

[0075] It was therefore evident that the specific process of the invention, employing a wet treatment with a vinyl polymer and a fatliquor, followed by vacuum treatment, allowed to obtain leather with the desired properties, extremely versatile for many different applications, such as the production of soft shoe soles.

Claims

CLAIMS1 . A process comprising:(i) a wet treatment of tanned leather comprising the following steps:(a) bringing the tanned leather into contact with at least one vinyl polymer;(b) bringing the tanned leather into contact with at least one fatliquor; and,(ii) subjecting the tanned leather obtained from step (i) to a vacuum treatment.

2. The process according to claim 1 , wherein said step (a) is performed at a temperature ranging from 20 to 40 °C, preferably from 25 to 35 °C, more preferably approximately 30 °C.

3. The process according to claim 1 or 2, wherein said vinyl polymer is an acrylic polymer.

4. The process according to any one of claims 1 to 3, wherein said vinyl polymer is used in an amount of at least 2% by weight with respect to the dry weight of the tanned leather.

5. The process according to any one of claims 1 to 4, wherein said tanned leather has a thickness equal to or greater than 5 mm and wherein said vinyl polymer is added in an amount of at least 5% by weight with respect to the dry weight of the tanned leather.

6. The process according to any one of claims 1 to 5, wherein in said step (b), the fatliquor is selected from the group consisting of sulfonated oil, sulfited oil, and sulfated oil.

7. The process according to any one of claims 1 to 6, wherein in said step (b), the fatliquor is of vegetable, animal, or mineral origin, preferably is an animal-origin sulfited oil, more preferably is a fish-origin sulfited oil.

8. The process according to any one of claims 1 to 7, wherein said step (b) is conducted at a temperature ranging from 30 to 50 °C, preferably at a temperature of approximately 40°C.

9. The process according to any one of claims 1 to 8, wherein said fatliquor in said step (b) is used as a formulation comprising at least one surfactant.

10. The process according to any one of claims 1 to 9, wherein said fatliquor in said step (b) is used in an amount equal to at least 2% by weight with respect to the dry weight of the tanned leather.11 . The process according to any one of claims 1 to 10, wherein the said process is performed according to the sequence of steps (a), (b), and (i) or, alternatively, according to the sequence of steps (b), (a), and (i).

12. The process according to any one of claims 1 to 11 , wherein said step (i) is performed at a temperature ranging from 35 to 55 °C, preferably at a temperature ranging from 40 to 50 °C, more preferably at a temperature of approximately 45 °C.

13. The process according to any one of claims 1 to 12, wherein said vacuum treatment has a duration ranging from 2 to 6 minutes, preferably from 3 to 5 minutes.

14. Leather obtainable by the process according to any one of claims 1 to 13.

15. A shoe sole made with the leather according to claim 14.

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